In recent years, rapid technical development in the electronics field has been promoting the reduction of the size and weight of electronic appliances. As a result, portable and cordless electronic appliances are increasing, and therefore there also is high demand for the reduction of the size and weight of the secondary power sources driving them. In order to satisfy these demands, lithium secondary batteries having a high energy density are being developed. In addition, ultrathin and lightweight secondary batteries using aluminum laminate film as the container member are also being developed and commercialized, recently.
In the secondary battery using the aluminum laminate container member, the battery thickness changes due to the volume expansion and contraction of the electrodes associated with charge and discharge. There is a problem in that as a result of this, the battery becomes twisted, and the distance between the electrodes increases thereby increasing battery resistance, resulting in the deterioration in battery characteristics.
A battery that can avoid these problems has been developed, in which lithium titanate is used as the material type for the negative electrode active material. Lithium titanate barely has any volume change associated with charge and discharge, and as a result, change in the battery thickness is extremely small. The above-described problems are solved by using this compound as the negative electrode active material.